One of the strongest correlates of male sexual orientation is sexual arousal to male versus female stimuli. Subjectively and genitally, gay men respond much more strongly to sexual stimuli depicting men than women, and heterosexual men show an opposite pattern. The investigators refer to the tight linkage between sexual orientation and sexual arousal patterns as "target specificity." There has been inadequate attention to the question of whether female sexual orientation is target specific. However, some research to data, including our own preliminary data, suggests that target specificity is much weaker for women than for men. This is particularly true of genital sexual arousal. To date research has failed to identify any aspect of sexual stimuli, including the sex of individuals depicted in the stimuli, that correlates reliably with female sexual orientation. One interpretation is that female genital arousal is provoked by a broad range of sexual stimuli. The investigators will assess the subjective and genital arousal of 180 lesbian, bisexual, and heterosexual women as they watch erotic video clips of lesbian, gay, or heterosexual interactions. They will also include a sexual stimulus depicting nonhuman animals, which we expect to be nonarousing, in an attempt to demonstrate at specificity of female genital response. If female target specificity exists, then lesbians should be most aroused by lesbian stimuli, and heterosexual women should be most aroused to the gay male stimuli, with bisexual women showing an intermediate pattern. The investigators argue that results will inform psychological theories of female sexual orientation regardless of specific outcome. This proposed study represents a marked departure from the principal investigator's previous work, which has primarily focused on the genetic and developmental origins of male and female sexual orientation.